1. Field of the Invention
This invention relates to endodontic instruments for treating of pulp canals and to a means for accurately, reliably and quickly adjusting the working length of such instruments.
2. Description of the Prior Art
Root canal therapy on endodontically involved teeth routinely involves the removal of the pulp from the root canal. This is conventionally accomplished by initially drilling the tooth to the pulp chamber, then reaming the canal with an elongated thin file, reamer, broach, or the like instrument made from a high strength, resilient metal capable of sufficient flexing to following the normal curvatures of the root canal. In the use of these instruments, referred to generally hereinafter as root canal files, extreme care must be taken to avoid penetration beyond the root canal to avoid injury and possible infection of the adjacent periodontal tissue and bone structure. At the same time, it is important to remove all of the pulp tissue from the canal to avoid the possibility of involvement of the root canal and the adjacent periodontal tissue subsequent to completion of the root canal treatment.
The length of the tooth involved, as well as the length of the root canal, is accurately determined by means of X-rays, and various techniques and devices have been devised in the past for limiting the depth of penetration of the root canal files to the root tip. Thus, many dentists employ a stop member which is penetrated by the root canal file for the desired distance, with the stop member being positioned to engage the top of the tooth to limit penetration. However, these stop members, normally made of a semi-rigid thermoplastic material, are easily displaced, particularly in working within the limited area of a patient's mouth and considering the relatively small size of the instruments involved.
It has also been proposed to provide screw threads on the shaft of the file, with a nut threaded onto the file to act as a stop. Again, however, manipulation of the file within a patient's mouth can easily result in the nut being moved on the shaft.
Another device, in common use, comprises a metal handle having movable jaws which are clamped onto the shaft of the handle by a threaded nut in a chuck-like arrangement, with the end of the handle and the chuck nut acting as the stop member. However, tightening of the chuck with sufficient force to avoid slippage was not always accomplished, particularly since there is a tendency to tighten the very small nut of the chuck by finger pressure only rather than to use the very small wrench to tighten the nut. Also, movement of the chuck nut during tightening inherently produced a change in the projecting length of the working portion of the file, making accurate measurement of the tool difficult.